This invention relates to the field of plastic optical fibers or synthetic optical fibers as they are also referred to in the art. More particularly, the invention relates to an improved method of making such fibers.
A prior method of making optical plastic fibers is illustrated in U.S. Pat. No. 3,472,921 and involves the injection of hot plasticized polystyrene into a pre-extruded acrylic sheath or tube. The method has the disadvantage that as a result of the temperature drop in the injected material, there is produced a gradient of styrene variability along the length of the sheath. Also, the viscosity changes of the injected plastic material along the length of the sheath will cause variance in the manner in which the injected material will adhere to the walls of the sheath along its length. In some cases there will be no adherence while in other cases there will be a meeting of the plastics or the causing of pearlization. In other words, the prior art methods have not produced a satisfactory interface between the core and the sheath in terms of quality and homogeneity throughout the length thereof.